City go back to United's home ground on Monday for the first time since Mancini's team inflicted the heaviest defeat of Sir Alex Ferguson's managerial career upon him: 6-1 derby victory in October 2011.

City triumphed in both league derbies last season as they went on to take the title on goal difference from United, but the defending champions are 15 points adrift of their neighbours now.

Indeed, United have eased their way ahead of their rivals in the New Year as they won 3-2 at the Etihad Stadium in December with an injury-time decider from Robin van Persie.

Mancini, though, believes the league table as it stands is not a real reflection of his side's abilities and efforts, saying: "It is not a true table."

When City beat United last April, they went top of the Premier League, whereas now Mancini has admitted it is impossible for them to win the division.

"The difference is that we score 20 goals less than last year," he said. "This is the only difference: we score less goals than last year. We concede the same and we have the best defence, we are missing only these goals. We had a lot of injuries, we lost Sergio [Aguero], we lost Mario [Balotelli, injured and then sold]. Mario scored 15 goals last season."

While a win would do little to stop the title heading back to Old Trafford eventually,
Mancini also said a repeat of last season's win won't happen and believes it is a once-in-a-century result, saying: "This is impossible. This can happen [once] every 100 years."

Mancini had hoped to sign Van Persie last summer, but the goals have dried up for the United top scorer, who has not struck in his last nine club matches. "We hope it will be 10 games," Mancini added.

The City manager said he is still wary of the Dutchman, explaining: "He can score in every moment in every game. This can happen for every striker: you can score every game for 20 games then [for] five, six, seven games you don't score."

City have no new injury worries for Monday's game, with Jack Rodwell still sidelined. Maicon and Micah Richards played for their Elite Development Squad on Wednesday but will not be involved. Mancini added: "I think in 10 days both will be ready."